Planetary gearbox having compliant journal bearings

ABSTRACT

A planetary gear train for an aircraft engine, has: a sun gear; planet gear assemblies having main gears meshed with the sun gear, fore lateral gears and aft lateral gears disposed on opposite sides of the main gears and rotating therewith; journal bearings rotatably supporting the planet gear assemblies for rotation about rotation axes, gaps defined between the journal bearings and the planetary gear assemblies; a planet carrier supporting the journal bearings; a fore ring gear meshed with the fore lateral gears; an aft ring gear meshed with the aft lateral gears; and a lubrication system extending within the planet carrier and hydraulically connected to the gaps between the journal bearings and the planet gear assemblies.

TECHNICAL FIELD

The application generally relates to aircraft engines and, moreparticularly, to gearboxes used in an aircraft engine such as a gasturbine engine.

BACKGROUND OF THE ART

Turboprops are gas turbine engines coupled to a propeller via areduction gearbox. Turbofan engines may also use a gearbox to drive thefan at a different speed than the engine, and other gas turbine enginetypes may employ gearboxes to step up or step down speed overcompressors. In the turboprop example, a reduction gearbox is used toreduce the rotational speed of the propeller relative to the turbine andto increase the torque generated by the turbine. In some gearboxes, inorder to increase the power to weight ratio, bearings supporting thegears may have an increased length. The length of the bearings may causethe load to concentrate on extremities of the bearings.

SUMMARY

In one aspect, there is provided a planetary gear train for an aircraftengine, comprising: a sun gear; planet gear assemblies having main gearsmeshed with the sun gear, fore lateral gears and aft lateral gearsdisposed on opposite sides of the main gears and rotating therewith;journal bearings rotatably supporting the planet gear assemblies forrotation about rotation axes, gaps defined between the journal bearingsand the planetary gear assemblies; a planet carrier supporting thejournal bearings; a fore ring gear meshed with the fore lateral gears;an aft ring gear meshed with the aft lateral gears; and a lubricationsystem extending within the planet carrier and hydraulically connectedto the gaps between the journal bearings and the planet gear assemblies.

In another aspect, there is provided an aircraft engine comprising ashaft drivingly engaged to a load via a planetary gear train, theplanetary gear train having a sun gear, planet gear assemblies includingmain gears meshed with the sun gear, fore lateral gears and aft lateralgears disposed on opposite sides of the main gears and rotatingtherewith, journal bearings rotatably supporting the planet gearassemblies for rotation about rotation axes, gaps defined between thejournal bearings and the planetary gear assemblies, a planet carriersupporting the journal bearings, a fore ring gear meshed with the forelateral gears, an aft ring gear meshed with the aft lateral gears, theshaft drivingly engaged to one of the sun gear, the planet carrier, andthe fore and aft ring gears, the load drivingly engaged to another oneof the sun gear, the planet carrier, and the fore and aft ring gears,and rotation of a remaining one of the sun gear, the planet carrier, andthe fore and aft ring gears being limited, the gaps between the journalbearings and the planet gear assemblies hydraulically connected tolubricant conduits of the planetary gear train.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a schematic cross-sectional view of a portion of the gasturbine engine illustrating a gear train;

FIG. 3 is a schematic tri-dimensional view of the gear train of FIG. 2;

FIG. 4 is a schematic cross-sectional view along line 4-4 of the geartrain of FIG. 3;

FIG. 5 is a sectional view of a portion of FIG. 2; and

FIG. 6 is a schematic cross-sectional view of a gear train in accordancewith another embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight and configured for driving a load 12, suchas, but not limited to, a propeller or a helicopter rotor. Depending onthe intended use, the engine 10 may be any suitable aircraft engine, andmay be configured as a turboprop engine or a turboshaft engine. The gasturbine engine 10 generally comprises in serial flow communication acompressor section 14 for pressurizing the air, a combustor 16 in whichthe compressed air is mixed with fuel and ignited for generating anannular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases.

The exemplary embodiment shown in FIG. 1 is a “reverse-flow” enginebecause gases flow from the inlet 17, at a rear portion of the engine10, to the exhaust outlet 19, at a front portion of the engine 10. Thisis in contrast to “through-flow” gas turbine engines in which gases flowthrough the core of the engine from a front portion to a rear portion.The engine 10 may be a reverse-flow engine (as illustrated) or athrough-flow engine.

In the illustrated embodiment, the turbine section 18 has ahigh-pressure turbine 18A in driving engagement with a high-pressurecompressor 14A. The high-pressure turbine 18A and the high-pressurecompressor 14A are mounted on a high-pressure shaft 15. The turbine 18has a low-pressure turbine, also known as power turbine 18B configuredto drive the load 12. The power turbine 18B is configured to drive alow-pressure compressor 14B through a low-pressure shaft 22. A reductiongearbox 20 is configured to connect the low-pressure shaft 22 thatsupports the power turbine 18B to a shaft 24 that is in drivingengagement with the load 12, while providing a reduction speed ratiotherebetween. Although a reduction gearbox is discussed in the exemplaryembodiments herein, the skilled reader will appreciate that the presentteachings are not limited to reduction gearboxes.

The reduction gearbox 20 allows the load 12 to be driven at a givenspeed, which is different than the rotational speed of the low-pressureturbine 18B. The reduction gearbox 20 allows both the load 12 and thelow-pressure turbine 18B to rotate at their respective optimal speedwhich are different. In the embodiment shown, the reduction gearbox 20is axially mounted at the front end of the engine 10.

For lubrication purpose, the gas turbine engine 10 includes alubrication system S that is fluidly connected to the reduction gearbox20 via suitable connections, such as via pipes S′, hoses, and the like.As described herein below with reference to FIG. 5, the lubricationsystem S may be used to supply oil to create a film of lubricant betweenstatic and rotating parts of the reduction gearbox 20.

Now referring to FIGS. 1-4, the reduction gearbox 20 comprises a geartrain 30 of the planetary type, also known as planetary gear train,epicyclic gear train, epicyclic gearbox, etc, but referred to as a geartrain 30 herein for clarity. It is understood that the gear train mayhave an epicyclic configuration or a star-type epicyclic configurationdepending of which component of the gear train is the input, which isthe output, and which is held stationary.

The gear train 30 has a sun gear 32 mounted on a sun gear connector 34configured to be connected to a layshaft 22 a (FIG. 2) that is connectedthe low-pressure shaft 22. In an alternate embodiment, the sun gear 32is mounted directly onto the layshaft 22 a that is connected to thelow-pressure shaft 22. The layshaft 22 a, also known as a torque shaft,is configured to allow flexibility from deflection or from othercontributor between the turbine section 18 and the reduction gearbox 20.In operation, the layshaft 22 a is designed to twist along itsrotational axis by a certain amount. The twist of the layshaft 22 a maybe monitored to indicate the actual torque that it transmits. The geartrain 30 further has a set of planet gear assemblies 36 rotatablymounted on shafts 38—three planet gear assemblies 36 are shown, althoughthe gear train 30 could have two or more planet gear assemblies 36. Inthe embodiment shown, all shafts 38 of the set of planet gear assemblies36 are connected to a planet carrier 40, the planet gear assemblies 36rotating onto the shafts 38. In a particular embodiment, the gear train30 comprises a plurality of planet gear assemblies 36. At least some ofthe plurality of assemblies 36 are mounted on the planet carrier 40,while others may simply rotate while not being connected to the planercarrier 40. In the illustrated embodiment, bearings 42 are disposedbetween the shafts 38 and the planet gear assemblies 36. The bearings 42are shown as plain oil film bearings. In the illustrated embodiment, theplanet carrier 40 has a connector 44 adapted to be coupled to the shaft24 of the load 12. Alternatively, the planet carrier 40 may be mounteddirectly to the shaft 24. In an alternate embodiment, the planet carrier40 is a zero-twist carrier to reduce twist deflection under torque bydriving the planet gear assemblies 36 from an axial positioncorresponding to a symmetry plane of the planet gear assemblies 36. In aparticular embodiment, the zero-twist carrier is as described in U.S.Pat. No. 6,663,530 which is incorporated herein by reference in itsentirety. Alternatively, radial stiffness of the shaft 38 may be variedalong its axis to reduce the deflection that is transmitted to theplanet gear assemblies 36.

Each planet gear assembly 36 has a main gear 46, fore and aft lateralgears 48 disposed on opposite sides of the main gear 46. The fore andaft lateral gears 48 rotate integrally with the main gears 46. The maingears 46 are meshed with the sun gear 32. In the illustrated embodiment,the main gears 46 and the sun gear 32 are spur gears, but other types ofgears may be used, such as helical gears. In the embodiment shown, adiameter 50 of the sun gear 32 is inferior to a diameter 52 of the maingears 46 to create a first rotational speed ratio to the gear train 30,between the sun gear 32 and the main gears 46 of the planet gearsassemblies 36. As shown in FIGS. 4 and 5, the main gear 46 and the foreand aft lateral gears 48 may share a common one of the plain bearing 42.Accordingly, in the set up shown in the figures, the presence ofmultiple gears on the same shaft 38 may result in a longer plain bearingthan for prior art planetary gearboxes.

Ring gears 54 are meshed with the fore and aft lateral gears 48 of theplanet gears assemblies 36. The ring gears 54 consist of two halves andare disposed symmetrically on each side of the main gears 46 so that thereaction load on the bearings 42 is equalised along their longitudinalaxis. The gears 48 and 54 may be spur gears (internal spur gear in thecase of the ring gear 54). In the illustrated embodiment, the lateralgears 48 and the ring gears 54 are helical gears. Helical gears may bequieter. In a particular embodiment, teeth of the fore lateral gear areangled in an opposite way relative to teeth of the aft lateral gear suchthat the fore and aft lateral gears are mirrored relative to oneanother. In operation, the main gears 46 of such a particular embodimentself-center under torque relative to the sun gear 32. This may enhancethe load sharing between the ring gears 54. In the embodiment shown, adiameter 56 of the lateral gears 48 is inferior to the diameter 52 ofthe main gears 46. Accordingly, a second rotational speed ratio betweenthe planet gear assemblies 36 and the ring gears 54, or between theplanet gears assemblies 36 and the planet carrier 40, is generated inthe gear train 30.

The gear train 30 provides a rotational speed ratio between the sun gear32 and the planet carrier 40 that could require at least twoconventional gear trains to achieve. In a particular embodiment, lessmoving parts are required which may lead to cost and weight reduction ofthe gas turbine engine 10. Furthermore, the moving parts of such gearboxrequire lubrication. By having fewer parts, less oil may be required.This may reduce the capacity of the required oil system and, becauseless heat is generated, the size of the required heat exchanger used tocool down the oil of the reduction gearbox 20 may be reduced. In aparticular embodiment, a total length of the gas turbine engine 10 maybe reduced by having the gear train 30 as described herein instead of atleast two conventional gear trains disposed in series to achieve a speedreduction ratio equivalent to the one of the gear train 30.

In the illustrated embodiment, the turbine shaft 22 is connected to thesun gear 32. The propeller shaft 24 is connected to the connector 44 ofthe planet carrier 40, for instance by spline connection. In such anembodiment, corresponding to a planetary arrangement, rotation of thering gears 54 is limited, preferably blocked, as the ring gears 54 arefixed to a structure of the gas turbine engine 10 as shown in FIG. 2. Itis understood that limiting rotation of the ring gears 54 comprisescompletely blocking the rotation of said ring gears. The speed reductionratio is defined as the rotational speed of the shaft 22 over therotational speed of the shaft 24. Such an embodiment provides thehighest speed reduction ratio and the highest torque increase betweenthe shafts 22 and 24 that is possible to achieve with the gear train 30.In this arrangement, the shafts 22 and 24 rotate in the same directionrelative to one another.

In an alternate embodiment, a star arrangement may be used. In a stararrangement, rotation of the planet carrier 40 is limited and thepropeller shaft 24 is operatively connected to the ring gears 54. It isunderstood that limiting rotation of the planet carrier 40 comprisescompletely blocking the rotation of said carrier. In this alternateembodiment, the ring gears 54 are both mounted and linked to thepropeller shaft 24. The total speed reduction ratio of the stararrangement would be less than the speed reduction ratio of the fixedconfiguration of the ring gears 54 as described above. In this alternateembodiment, the propeller shaft 24 and the turbine shaft 22 rotate inopposite directions.

By having two ring gears 54 disposed on opposite sides of the main gears46 the load is symmetrically distributed relative to a plane P, to whichan axis of rotation A of the sun gear 32 is normal, the plane P beinglocated half way through a thickness T of the main gears 46. Bysymmetrically distributing the load, the gear train may be adapted towithstand higher torques and may be adapted to use plain bearingsinstead of heavier and more expensive rolling element bearings.

The gear train 30 may be used in a plurality of applications, other thangas turbine engines, in which a rotational speed ratio between tworotating components is required. In such an embodiment, an input isprovided to one of the sun gear 32, the planet carrier 40, and the ringgears 54 and an output is connected to another one of the sun gear 32,the planet carrier 40, and the ring gears 54. Rotation of a remainingone of the sun gear 32, the planet carrier 40, and the ring gears 54,that is not connected to the input or the output, is limited. In anembodiment, the input is the sun gear 32, the output is the planetcarrier 40, and rotation of the ring gears 54 is blocked. According toanother embodiment, the input is the sun gear 32, the output is the ringgears 54, and rotation of the planet carrier 40 is blocked. Suitablemeans are used for transmitting rotation of the ring gears 54 to theshaft 24. Other configurations are contemplated.

The gear train 30 is adapted to change a rotational speed of a rotatingcomponent relative to another rotating component. In the illustratedembodiment, the rotating component is the low-pressure shaft 22 and theother rotating component is the shaft 24. In the illustrated embodiment,the shaft 24 is connected to the load 12, but it may be connected to anyother suitable component such as, but not limited to, a helicopterrotor, or an accessory of the gas turbine engine 10.

To change the rotational speed of the shaft 24 relative to the shaft 22,the gear train 30 first receives a torque of the low-pressure shaft 22via the sun gear 32. Then, the torque is transmitted to main gears 46 ofa set of planet gear assemblies 36 meshed with the sun gear 32. Eachplanet gear assembly 36 of the set of planet gear assemblies 36comprises aft and fore lateral gears 48 disposed on opposite sides ofthe main gear 46. In the illustrated embodiment, a first rotationalspeed ratio is generated by having a diameter 50 of the sun gear 32inferior to a diameter 52 of the main gears 46.

The torque is then transmitted from the fore and aft lateral gears 48 toone of the planet carrier 40 and the ring gears 54 meshed with the foreand aft lateral gears 48, while another one of the planet carrier 40 andthe ring gears 54 is fixed so as not to rotate. A second rotationalspeed ratio is generated by having the diameter 56 of the fore and aftlateral gears 48 inferior to the diameter 52 of the main gear 46. Athird rotational speed ratio is generated by the interaction of the foreand aft lateral gears 48 with the ring gears 54. The diameters 50, 52,and 56 and/or other gear parameters may be tuned to achieve the desiredreduction ratio. Parameters of the diameter of the ring gears 54 may betuned to achieve the desired reduction ratio. Herein, gear parameters isunderstood to mean any parameters known in the art, such as, toothcount, tooth pitch, and so on.

Referring now also to FIG. 5, only one of the planet gear assemblies 36and bearings 42 is described herein below using the singular form.However, it is understood that the below description may apply to two ormore (e.g., all) of the planet gear assemblies 36 and bearings 42 of thegearbox 20.

The bearing 42 is a journal bearing that may include a sleeve 60 and ajournal 62, also referred to as a journal shaft. The sleeve 60 may beused to form one surface of the journal bearing. The sleeve 60 may bedisposed radially outwardly to the journal 62 relative to a rotationaxis A′ of the planet gear assembly 36 defined by the shaft 38. Both ofthe sleeve 60 and the journal 62 are disposed around the shaft 38. Inthe embodiment shown, the sleeve 60, if present, is tight fitted insidethe planet gear assembly 36 (or force fitted, press fitted, secured,etc). Accordingly, the sleeve 60 rotates concurrently with the planetgear assembly 36, i.e., the gears 46 and 48. The sleeve 60 may be coatedat its internal diameter, where it interfaces with the journal 62 tocreate the journal bearing 42.

The lubrication system S (FIG. 1) is used to inject a flow F oflubricant within an annular gap G disposed radially between the sleeve60 and the journal 62 relative to the axis A′. In the embodiment shown,the lubrication system S injects the lubricant via a first conduit 38 aand a second conduit 36 a. The first conduit 38 a extends axially withinthe shaft 38 and has an inlet 38 b in fluid flow communication with thelubrication system S. The first conduit 38 a may have an outlet 38 c influid flow communication with an inlet 36 b of the second conduit 36 a.The second conduit 36 a extends through the journal 62, from a radiallyinner face 62 a to a radially outer face 62 b thereof. The inlet 36 bmay be an annular space to which the outlet 38 c opens. The secondconduit 36 a has an outlet 36 c that is radially outward of the secondconduit inlet 36 b. The second conduit inlet and outlet 36 b, 36 c maybe located at the journal's radially inner and outer surfaces 62 a, 62b, respectively. The second conduit 36 a opens to the gap G between thesleeve 60 and the journal 62. In operation, the lubrication system Ssupplies the gap G with lubricant under pressure to allow the formationof a pressurized film of lubricant between the journal 62 and the sleeve60. The journal 62 may float relative to the sleeve 60 by way of thefilm of lubricant in the gap G.

In the depicted embodiment, to accommodate the fore and aft lateralgears 48 as well as the main gear 46, an axial length L of the planetgear results in a journal bearing 42 supporting the planet gear assembly36 is more than that of a journal bearing supporting a planet gear of aconventional planetary gearbox. Moreover, in a particular embodiment,the axial length L has to be greater than a sum of axial lengths of thefore and aft lateral gears 48 and of the main gear 46 because an axialdistance between teeth of both the fore and aft lateral gears 48 andteeth of the main gear 46 is preferably maintained to allow a cuttingtool to machine the teeth.

The increased length of the disclosed journal bearing 42 compared tothat of conventional planetary gearbox journal bearings induces a loadconcentration at axial extremities of the journal bearing 42. In aparticular embodiment, the load concentration at the axial extremitiesis such that the film of lubricant is not able to sustain the pressurewhich may lead to distress. This load concentration may be caused by theincreased stiffness created by the cooperation of the fore and aftlateral gears 48 with the ring gears 54. In other words, the fore andaft lateral gears 48 combined with the ring gears 54 may cause the gearassembly 36 to be stiff at the axial extremities.

Accordingly, undercuts may be defined in the planet gear assembly 36 toincrease compliance of such an assembly to loads. However, a radialthickness of the planet gear assembly 36, at a location where the foreand aft lateral gears 48 are meshed with the ring gears 54, ispreferably kept above a certain value to have sufficient material tomachine teeth of the fore and aft lateral gears 48. Furthermore, theradial thickness may have to be kept above a certain value to be able towithstand the load imparted to the fore and aft lateral gears 48. Thus,for the disclosed gearbox 30, it may not be possible to add theundercuts at the ends of the planet gear assembly 36.

Increasing a diameter of the fore and aft lateral gears 48 to maintainthis radial thickness and allow undercuts to be machined may also not bea viable option as it would change the speed ratio imparted by thegearbox 30. Alternatively, increasing the diameter of the gears 48 tomaintain this radial thickness might not be a viable option as it mightresult in a larger gear train envelope diameter, which may not be anoption for all gas turbine engines.

Still referring to FIG. 5, in view of the above, undercuts 64 a, 64 bare located at the journal 62 of the journal bearing 42. In theembodiment shown, the journal bearing 62 defines two undercuts 64 a, 64b configured for allowing radial compliance or flexibility to thejournal bearing 42. Each of the two undercuts 64 a, 64 b is located at arespective one of journal first and second axial end faces 62 c, 62 d.Each of the two undercuts 64 a, 64 b defines an annular channel Ccircumferentially extending around the rotation axis A′ of the planetgear assembly 36. The first undercut 64 a extends from the first axialend face 62 c toward the second axial end face 62 d. The second undercut64 b extends from the second axial end face 62 d toward the first axialend face 62 c. In the depicted embodiment, the two undercuts 64 a, 64 bare symmetrical relative to one another about the plane P disposedaxially at equal distance from the two axial end faces 62 c, 62 d. Avector of the axis of rotation A′ is normal to the plane P. The plane Pis a mid-plane of the main gear 46. However, the two undercuts 64 a and64 b may not be symmetrical relative to one another.

Each of the two undercuts 64 a, 64 b has a height H at the axial endfaces 62 c, 62 d. The height H is defined radially relative to the axisA′. A depth D is defined axially relative to the axis A′. The height Hand the depth D are selected such that the stiffness of the journalbearing 42 to radial loads is adjusted on the axis A′ defined by theshaft 38 to make it compliant to journal bearing forces so that that theresultant journal bearing load may be better distributed along the axisA′ as compared to a configuration lacking such undercuts 64 a, 64 b.This may result in the continuous inward tapering shape or in any otherappropriate shape.

In the embodiment shown, a ratio of the height H over the depth D rangesfrom 0.2 to 1.0. Preferably, the height H over depth D ratio H/D rangesfrom 0.35 to 0.5. In the embodiment shown, a height H over length Lratio H/L ranges from 0.02 to 0.2, preferably from 0.05 to 0.1. In theillustrated embodiment, a depth D over length L ratio D/L ranges from0.1 to 0.3, preferably from 0.15 to 0.2.

To determine the depth D and height H of the undercuts 64 a, 64 b suchthat the journal bearing 42 may be used in all engine operatingconditions and may meet the durability requirements, an iterative methodmay be used. The method includes defining a geometry for the journalbearing 42 including the planet gear assembly 36 and the shaft 38 basedon the requirements. A numerical model of this geometry is preparedusing Finite Element Method (FEM). The method may further includeanalyzing both journal and planet deformation compliance andconsequently optimize geometry. The compliance, which corresponds to theinverse of the stiffness, is calculated on the geometry at each point ofthe journal bearing 42. The calculated compliances are stored in acombined compliance matrix. Herein, “combined” implies that the matrixtakes into consideration stiffness of both the shaft and the planet. AnElastoHydroDynamic (EHD) analysis is performed to calculate lubricantfilm distribution (film thickness, pressure, temperature, flow, etc).Based on the results of the EHD analysis, the geometry is modified tooptimize the lubricant film parameters. The steps described above arerepeated until the journal bearing 42 is matched to the planet gearassembly 36.

In a particular embodiment, the disclosed gear train 30 having two ringgears 54 may create a more equal longitudinal load distribution and mayenable the use of the journal bearing.

Referring now to FIG. 6, another embodiment of a gear train is generallyshown at 130. The gear train 130 shown in FIG. 6 may be referred to as astar-type planetary gear train. In the embodiment shown in FIG. 6, theplanet carrier 40 is fixed such that it does not rotate and the ringgears 154 are rotatable. In other words, the output of the gear train130 is the ring gears 154. The gear train 130 further includes a ringgear connector 70 configured for mechanically linking the ring gears 154to the shaft 24.

Each of the ring gears 154 includes a geared section 154 a in meshingengagement with a respective one of the fore and aft lateral gears 48and a connector sections 154 b. The connector sections 154 b are securedto the geared sections 154 a and extend radially away therefrom. In theembodiment shown, the geared and connector sections 154 a, 154 b aremonolithic. Other configurations are contemplated.

The ring gear connector 70 has a proximal end 70 a secured to the shaft24 via the connector 44. The ring gear connector 70 has a distal end 70b that is securable to the ring gears 154. More specifically, each ofthe connector sections 154 b of the ring gears 154 has a distal endrelative to a distance from the fore and aft lateral gears 48. Thedistal ends are secured to the distal end 70 b of the ring gearconnector 70.

As shown in FIG. 6, an assembly of the connector sections 154 b of thering gears 154 has an inverted U-shape to allow passage of the main gear46 such that teeth of the main gears 46 are free of contact with theconnector sections 154 b of the ring gears 154.

In the embodiment shown, the ring gear connector 70, and the connectorsections 154 b of the ring gears are annular and extendcircumferentially all around the axis of the shaft. Other configurationsare contemplated without departing from the scope of the presentdisclosure.

Embodiments disclosed herein include:

A. A planetary gear train for an aircraft engine, comprising: a sungear; planet gear assemblies having main gears meshed with the sun gear,fore lateral gears and aft lateral gears disposed on opposite sides ofthe main gears and rotating therewith; journal bearings rotatablysupporting the planet gear assemblies for rotation about rotation axes,gaps defined between the journal bearings and the planetary gearassemblies; a planet carrier supporting the journal bearings; a forering gear meshed with the fore lateral gears; an aft ring gear meshedwith the aft lateral gears; and a lubrication system extending withinthe planet carrier and hydraulically connected to the gaps between thejournal bearings and the planet gear assemblies.

B. An aircraft engine comprising a shaft drivingly engaged to a load viaa planetary gear train, the planetary gear train having a sun gear,planet gear assemblies including main gears meshed with the sun gear,fore lateral gears and aft lateral gears disposed on opposite sides ofthe main gears and rotating therewith, journal bearings rotatablysupporting the planet gear assemblies for rotation about rotation axes,gaps defined between the journal bearings and the planetary gearassemblies, a planet carrier supporting the journal bearings, a forering gear meshed with the fore lateral gears, an aft ring gear meshedwith the aft lateral gears, the shaft drivingly engaged to one of thesun gear, the planet carrier, and the fore and aft ring gears, the loaddrivingly engaged to another one of the sun gear, the planet carrier,and the fore and aft ring gears, and rotation of a remaining one of thesun gear, the planet carrier, and the fore and aft ring gears beinglimited, the gaps between the journal bearings and the planet gearassemblies hydraulically connected to lubricant conduits of theplanetary gear train.

Embodiments A and B may include any of the following elements, in anycombinations:

Element 1: the planet carrier includes shafts secured to the planetcarrier, the journal bearings fixedly mounted on the shafts, the shaftsdefining shaft conduits of the lubrication system, the shaft conduitshaving shaft conduit outlets hydraulically connected to the gaps.Element 2: the shaft conduits extend along an entirety of an axiallength of the journal bearings relative to their respective rotationaxes. Element 3: the shaft conduit outlets and the journal conduits areaxially centered between opposed axial end faces of the journal bearingsrelative to the axial length of the journal bearings. Element 4: thejournal bearings define journal conduits extending from inner faces ofthe journal bearings to outer faces thereof, the journal conduits havingjournal conduit inlets connected to the shaft conduit outlets andjournal conduit outlets opening to the gaps. Element 5: the lubricationsystem includes journal conduits extending between inner faces of thejournal bearings and outer faces thereof, the journal bearings definingeach an annular space extending from the inner faces toward the outerfaces, the annular spaces extending circumferentially all around therotation axes, journal conduits inlets of the journal conduits being influid flow communication with the annular spaces. Element 6: the journalbearings are symmetrical about a plane normal to the rotation axes, themain gears being centered on the plane. Element 7: sleeves secured tothe planet gear assemblies, the gaps located between the sleeves and thejournal bearings. Element 8: a diameter of the main gears is differentthan that of the fore and aft lateral gears. Element 9: the diameter ofthe main gears is greater than that of the fore and aft lateral gears.Element 10: sleeves mounted to the planet gear assemblies, the gapslocated between the sleeves and the journal bearings. Element 11: thejournal bearings are fixedly mounted on shafts secured to the planetcarrier, the lubricant conduits including shaft conduits extendingwithin the shafts. Element 12: the shaft conduits extend along anentirety of a length of the journal bearings. Element 13: the shaftconduits define shaft conduit outlets in fluid flow communication withthe gaps, the shaft conduit outlets being apertures extending radiallythrough the shafts relative to the rotation axes. Element 14: the shaftconduit outlets are centered between axially opposed end faces of thejournal bearings. Element 15: the lubricant conduits include journalconduits extending from inner faces to outer faces of the journalbearings, the journal conduits having journal conduit inletscircumferentially aligned with the shaft conduit outlets and journalconduit outlets opening to the gaps. Element 16: the journal conduitsare axially centered between the opposed axial end faces of the journalbearings relative to the length of the journal bearings. Element 17:annular spaces extending from the inner faces to the outer faces of thejournal bearings, the annular spaces extending circumferentially allaround the rotation axes and are centered between the opposed axial endfaces of the journal bearings, the shaft conduit outlets hydraulicallyconnected to the journal conduit inlets via the annular spaces. Element18: each of the shaft conduits include at least two shaft conduitoutlets and each of the journal bearings include at least two journalconduits each hydraulically connected to a respective one of the atleast two shaft conduit outlets.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Still other modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

1. A planetary gear train for an aircraft engine, comprising: a sungear; planet gear assemblies having main gears meshed with the sun gear,fore lateral gears and aft lateral gears disposed on opposite sides ofthe main gears and rotating therewith; journal bearings rotatablysupporting the planet gear assemblies for rotation about rotation axes,gaps defined between the journal bearings and the planetary gearassemblies; a planet carrier supporting the journal bearings; a forering gear meshed with the fore lateral gears; an aft ring gear meshedwith the aft lateral gears; and a lubrication system extending withinthe planet carrier and hydraulically connected to the gaps between thejournal bearings and the planet gear assemblies.
 2. The planetary geartrain of claim 1, wherein the planet carrier includes shafts secured tothe planet carrier, the journal bearings fixedly mounted on the shafts,the shafts defining shaft conduits of the lubrication system, the shaftconduits having shaft conduit outlets hydraulically connected to thegaps.
 3. The planetary gear train of claim 2, wherein the shaft conduitsextend along an entirety of an axial length of the journal bearingsrelative to their respective rotation axes.
 4. The planetary gear trainof claim 3, wherein the shaft conduit outlets and the journal conduitsare axially centered between opposed axial end faces of the journalbearings relative to the axial length of the journal bearings.
 5. Theplanetary gear train of claim 2, wherein the journal bearings definejournal conduits extending from inner faces of the journal bearings toouter faces thereof, the journal conduits having journal conduit inletsconnected to the shaft conduit outlets and journal conduit outletsopening to the gaps.
 6. The planetary gear train of claim 1, wherein thelubrication system includes journal conduits extending between innerfaces of the journal bearings and outer faces thereof, the journalbearings defining each an annular space extending from the inner facestoward the outer faces, the annular spaces extending circumferentiallyall around the rotation axes, journal conduits inlets of the journalconduits being in fluid flow communication with the annular spaces. 7.The planetary gear train of claim 1, wherein the journal bearings aresymmetrical about a plane normal to the rotation axes, the main gearsbeing centered on the plane.
 8. The planetary gear train of claim 1,comprising sleeves secured to the planet gear assemblies, the gapslocated between the sleeves and the journal bearings.
 9. The planetarygear train of claim 1, wherein a diameter of the main gears is differentthan that of the fore and aft lateral gears.
 10. The planetary geartrain of claim 9, wherein the diameter of the main gears is greater thanthat of the fore and aft lateral gears.
 11. An aircraft enginecomprising a shaft drivingly engaged to a load via a planetary geartrain, the planetary gear train having a sun gear, planet gearassemblies including main gears meshed with the sun gear, fore lateralgears and aft lateral gears disposed on opposite sides of the main gearsand rotating therewith, journal bearings rotatably supporting the planetgear assemblies for rotation about rotation axes, gaps defined betweenthe journal bearings and the planetary gear assemblies, a planet carriersupporting the journal bearings, a fore ring gear meshed with the forelateral gears, an aft ring gear meshed with the aft lateral gears, theshaft drivingly engaged to one of the sun gear, the planet carrier, andthe fore and aft ring gears, the load drivingly engaged to another oneof the sun gear, the planet carrier, and the fore and aft ring gears,and rotation of a remaining one of the sun gear, the planet carrier, andthe fore and aft ring gears being limited, the gaps between the journalbearings and the planet gear assemblies hydraulically connected tolubricant conduits of the planetary gear train.
 12. The aircraft engineof claim 11, comprising sleeves mounted to the planet gear assemblies,the gaps located between the sleeves and the journal bearings.
 13. Theaircraft engine of claim 12, wherein the journal bearings are fixedlymounted on shafts secured to the planet carrier, the lubricant conduitsincluding shaft conduits extending within the shafts.
 14. The aircraftengine of claim 13, wherein the shaft conduits extend along an entiretyof a length of the journal bearings.
 15. The aircraft engine of claim14, wherein the shaft conduits define shaft conduit outlets in fluidflow communication with the gaps, the shaft conduit outlets beingapertures extending radially through the shafts relative to the rotationaxes.
 16. The aircraft engine of claim 15, wherein the shaft conduitoutlets are centered between axially opposed end faces of the journalbearings.
 17. The aircraft engine of claim 16, wherein the lubricantconduits include journal conduits extending from inner faces to outerfaces of the journal bearings, the journal conduits having journalconduit inlets circumferentially aligned with the shaft conduit outletsand journal conduit outlets opening to the gaps.
 18. The aircraft engineof claim 17, wherein the journal conduits are axially centered betweenthe opposed axial end faces of the journal bearings relative to thelength of the journal bearings.
 19. The aircraft engine of claim 18,comprising annular spaces extending from the inner faces to the outerfaces of the journal bearings, the annular spaces extendingcircumferentially all around the rotation axes and are centered betweenthe opposed axial end faces of the journal bearings, the shaft conduitoutlets hydraulically connected to the journal conduit inlets via theannular spaces.
 20. The aircraft engine of claim 19, wherein each of theshaft conduits include at least two shaft conduit outlets and each ofthe journal bearings include at least two journal conduits eachhydraulically connected to a respective one of the at least two shaftconduit outlets.